JP5352541B2 - Boss structure of work machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase strength of a junction between a sheet-metal member and a boss part in a work apparatus, in a boss structure of a work machine including the work apparatus having a rectangular cross-section constituted by the sheet member that is joined to the boss part by a welding part. <P>SOLUTION: A work machine includes a work apparatus that is swingably mounted on one end with a pivot, and has a rectangular cross-section constituted by a sheet member 9 that is joined to a boss part by a welding part 14. The boss part is welded to the sheet member via a flange portion 10a that is provided with a step portion 15 including a concave top and a convex bottom. The welding part 14 is arranged at a position apart from the step portion toward the sheet member. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a boss structure of a work machine, and more particularly to a structure of a boss portion in a boom or an arm of a hydraulic excavator.

  As a boss structure of a conventional work machine, there is one described in Patent Document 1. The thing of this patent document 1 tries to relieve | moderate the stress of a junction part using the bending stress which arises by carrying out the welding of a boss | hub with a side plate (plate material which comprises a boom).

Japanese Utility Model Publication No. 63-136041

In the above prior art, the stress on the back side of the boom is relieved because of the bending stress due to the mistake.
However, according to the analysis, the stress distribution on the back side of the boom, which has a mistake, shows that the stress changes sharply at the stepped part (missing part). In the conventional structure, the welded part has a sufficiently low stress. However, it was found that the stress is in a position where it can change sensitively.
Moreover, in the thing of patent document 1, although the stress on the front side of a boom is not considered, since the stress on the front side of the said level | step-difference part becomes high, there also existed a danger that a crack would generate | occur | produce from the front side of a welding part.

  An object of the present invention is to provide a working machine boss structure including a working device configured to have a rectangular cross section by a plate material and having a boss portion joined to the plate material by a welded portion, and the plate material in the working device. And improving the joint strength between the boss and the boss.

  In order to achieve the above object, the present invention is configured to have a rectangular cross section by a plate material, and in the boss structure of a working machine provided with a work device in which a boss portion is joined to the plate material by a welded portion, The boss portion is welded to the plate member via a flange portion, and a step portion is formed on the flange portion so that the front side is concave and the back side is convex. The welded portion is provided at a position separated from the side, and a backing material for preventing the weld metal from being burned out is provided on the back side of the welded portion, and the boss portion, the backing material, and the plate material And an insulative part is formed between each of the backing material and the backing material.

  Further, in the present invention, when the thickness of the plate material is t, the front end of the welded portion of the welded portion is located at a position 1t to 2t away from the plate material side end on the back side of the stepped portion. A welded portion may be provided.

  In the above, the thickness at the front end side of the collar portion to be welded is substantially the same as the thickness of the plate material to be joined, and the thickness of the stepped portion (the thickness between the front side and the back side of the stepped portion) is It is good to make it smaller than the plate | board thickness in a welding part.

Moreover, it is preferable to form the back side step inflection start portion closer to the welded portion than the front side step inflection start portion of the step portion.
Furthermore, it is preferable that the step portion of the boss portion is welded to the plate material in a state in which a stress relaxation treatment is performed in which the step portion is smoothly formed by machining or a grinder in advance.

  According to the present invention, since the tensile stress at the joint portion between the plate member and the boss portion configured to have a rectangular cross section can be relieved, the strength of the joint portion can be improved, and a crack is generated at the joint portion. A boss structure of a work machine that can prevent this can be obtained.

The front view which shows the whole structure of a working machine. Sectional drawing which looked at boom center boss vicinity from the front-back direction. The figure which expands and shows the A section of FIG. The figure explaining the stress distribution which generate | occur | produces on the bottom face of a structure when a tensile load acts on the structure which has a misalignment part. The figure explaining the stress distribution in a X direction from the front-end | tip of an unwelded part at the time of welding to the misplaced part of a structure. FIG. 4 is a diagram illustrating the first embodiment of the present invention and corresponding to FIG. 3. The figure explaining the stress distribution of the non-welding part vicinity in Example 1 of this invention. Sectional drawing which shows the example which applied Example 1 of this invention to the boom center boss | hub of the hydraulic shovel, and looked at the boom center boss vicinity from the front-back direction. The example which applied Example 1 of the present invention to the boom foot boss of a hydraulic excavator, and is the sectional view which looked at the neighborhood of the boom foot boss from the front-back direction.

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to a boss structure of a hydraulic excavator as a work machine.
First, the overall configuration of the work machine (hydraulic excavator) will be described with reference to FIG.

  In FIG. 1, reference numeral 1 denotes a lower traveling body of a hydraulic excavator, and an upper revolving body 2 is rotatably attached to an upper portion of the lower traveling body 1 via a revolving bearing. Is attached so that the working device 20 can move up and down (turn). The working device 20 includes a boom 3 that is pin-coupled to the revolving frame of the upper-part turning body 2, an arm 4 that is pin-coupled to the distal end side of the boom 3, and a bucket 5 that is pin-coupled to the distal end side of the arm 4. Etc. The boom 3, the arm 4 and the bucket 5 are rotated by a boom cylinder 6, an arm cylinder 7 and a bucket cylinder 8, respectively. The pins are held by brackets and bosses of the respective structures.

  Most of the structure constituting the working device (working arm) is formed in a rectangular cross section (box shape) by a plate material, and the boss is joined to the plate material by welding. A specific example is shown in FIG. FIG. 2 is a cross-sectional view of the vicinity of the boom center boss (boss portion) 10 as seen from the front-rear direction. As shown in FIG. 2, the left and right bosses 10 on which the flange portions 10 a are formed are joined together by pipes 12, and the flange portions 10 a of the left and right bosses 10 are joined to the plate material 9 of the structure of the boom 3 by welding. ing. The thickness t of the plate material 9 and the thickness of the collar of the boss 10 are substantially the same so that the acting load (force) is transmitted smoothly at this joint.

  Since the structure of the working device 20 has a rectangular cross section, a welding material 11 is provided on the inner surface of the welded portion between the boss 10 and the plate material 9 to prevent the weld metal from being melted, and then welded from the outside of the structure. Is done. However, since the backing material 11 remains after the welding, as shown in FIG. 3, an unwelded portion 13 is formed on the inner surface side of the welded portion. The tip of the welded portion 13 (weld bead side) concentrated stress and increased stress, and it was easy to become a starting point of crack generation. However, since the non-welded portion is the inner surface of the box-shaped structure, it is difficult to perform post-processing after welding.

  For this reason, the plate thickness of the plate material 9 is increased to relieve stress and the generation of cracks is prevented, but there is a problem that the weight increases because the plate thickness is increased. In addition, as in Patent Document 1 described above, it is also considered that a joint portion between the plate material and the boss is provided with a misalignment portion, and the stress of the joint portion is relieved by a bending stress caused by the misunderstanding.

  However, when the stress due to the misunderstanding is analyzed, as shown in FIG. 4, when a tensile load is applied to the structure having the misaligned portion, the compressive stress on the bottom surface (inside the structure) depends on the misunderstanding. It was found that the position away from the step portion 15 (X direction in FIG. 4) was larger than the step portion 15 and the compressive stress was sharply reduced in the step portion 15 portion. In the graph of FIG. 4, the horizontal axis indicates the distance X from the step portion 15, the + side is the distance in the X direction, the − side is the distance in the anti-X direction, and the ratio to the thickness t of the plate material. It represents the magnitude of the distance. The vertical axis indicates the magnitude of the compressive stress, and 0 indicates that the compressive stress increases toward the lower side without any compressive stress.

  For this reason, in the conventional structure as shown in Patent Document 1, as shown in FIG. 5, the tip 13a of the welded portion 13 is a place where stress is most relaxed (a portion where the compressive stress is large, where a tensile load was applied). Even in the case, it is not in a place where the tensile stress can be relieved), and it was found that the compression stress is sensitively lowered. In the graph of FIG. 5, the horizontal axis indicates the distance in the X direction from the tip of the non-welded portion on the plate material 9 side of the non-welded portion tip 13 a, and the ratio to the thickness t of the plate material 9. It represents the magnitude of the distance. The vertical axis indicates the magnitude of the compressive stress, and 0 indicates that the compressive stress increases toward the lower side without any compressive stress.

Moreover, in the thing of patent document 1, since the stress of the front side of a structure is not considered, since the tensile stress of the front side recessed part 15a of the said level | step-difference part 15 becomes high on structure, the toe part 14a of the weld bead 14 is high. Is located in the front-side recess 15a (see FIG. 4) of the step portion 15, there is a possibility that a crack may occur from the surface of the front-side recess.
Specific examples of the present invention for solving the above problems will be described below.

In this embodiment, as shown in FIG. 6, the configuration of the welded portion between the boss portion (boom center boss) 10 and the plate material 9 is as follows.
(1) The step portion 15 is provided in the collar portion 10a of the boss portion 10 so that the front side of the structure is concave and the back side is convex.
(2) The back side step inflection start portion 15c is formed closer to the welded portion (weld bead) 14 than the front side step inflection start portion 15b of the step portion 15.
(3) The plate thickness t of the flange portion 10a is made substantially the same as the plate thickness t of the plate material 9 to be joined, and the plate thickness of the stepped portion 15 is made smaller than the plate thickness of the welded portion.
(4) The step portion 15 of the boss portion 10 is welded to the plate member 9 in a state in which a stress relaxation treatment is performed in advance that is smoothly formed by machining or a grinder.

  In the present embodiment, with the above-described configuration, when a tensile load is applied to the step portion 15, the welded portion is deformed so as to bend to the front side. Thereby, since a large compressive stress is generated in the portion of the non-welded portion 13 on the back side, the tensile stress is hardly generated in the non-welded portion 13 and the strength can be improved. This will be described with reference to FIG.

  FIG. 7 is a diagram for explaining the stress distribution near the non-welded portion on the back side of the step portion 15 of the present embodiment shown in FIG. 6, and in the graph of FIG. The distance from the tip of the non-welded portion is shown as a reference, the + side is the distance on the plate material 9 side, the-side is the distance on the boss portion 10 side, and the size of the distance relative to the thickness t of the plate material 9 Represents. The vertical axis indicates the magnitude of the compressive stress, and 0 indicates that the compressive stress increases toward the lower side without any compressive stress. As shown in this figure, a large compressive stress is generated in the left and right non-welded portions 13a on the back surface of the weld bead 14, and as a result, a tensile stress that is a problem in strength is hardly generated. Strength can be improved. That is, cracks are likely to occur when the tensile stress increases, but if the compressive stress is large, even if various loads are applied during the operation of the hydraulic excavator, it is difficult for the tensile stress to be generated in the portion where the compressive stress is large. As a result, the occurrence of cracks can be prevented.

  Further, in the present embodiment, since the plate thickness of the step portion 15 is made smaller than the plate thickness of the welded portion, the step portion 15 becomes the highest stress concentration portion, and the deformation of the step portion 15 becomes large. The stress generated in is relaxed. Therefore, the occurrence of cracks from the toe portion 14a of the welded portion 14 can also be prevented.

Further, although the step 15 of the boss 10 has a large stress, the stress of the step 15 is also relieved by subjecting the boss 10 to stress relaxation processing in advance by machining or a grinder at the part stage. be able to.
Thereby, generation | occurrence | production of the crack in the whole level | step-difference part including a welding part can be prevented.

FIG. 8 shows a case where the above-described embodiment is applied to the boom center boss 10 (see FIG. 1) of the hydraulic excavator, and is a cross-sectional view of the vicinity of the boom center boss 10 as seen from the front-rear direction.
As shown in the drawing, the left and right boom center bosses (boss portions) 10 formed with the flange portions 10 a are connected by pipes 12, and the flange portions 10 a of the left and right boom center bosses 10 are the structures of the boom 3. The plate 9 is joined by welding. The thickness t of the plate member 9 and the thickness of the collar portion 10a of the boom center boss 10 are made substantially the same so that the acting load is transmitted smoothly at this joint portion. A welding material 11 is provided on the inner surface (back surface) of the welded portion between the boom center boss 10 and the plate material 9 to prevent the weld metal from being melted (blown out), and welding is performed from the outside of the structure. Since the welding metal melts, the backing material 11 is stuck to the back surface without being peeled off. For this reason, an unwelded portion 13 as shown in FIG. 6 is formed between the boom center boss 10 and the backing material 11 and between the plate material 9 and the backing material 11. The flange portion 10a of the boom center boss 10 is formed with a step portion 15 so that the front side is concave and the back side is convex.

  A pin (not shown) is inserted into the hole portion of the boom center boss 10 and coupled to the boom cylinder 6 (see FIG. 1). The force from the boom cylinder 6 is transmitted to the boom center boss 10 via the pins, and is transmitted from the boom center boss 10 to the plate material 9.

When the force is transmitted from the boom center boss 10 to the plate member 9, the step portion 15 is present, so that a bending moment is generated, and when a tensile load affecting fatigue strength is applied, the vicinity of the step portion 15 (including the welded portion) is the front side. Deforms to curve outward.
Therefore, the step portion 15 has a high stress on the front side, a low stress on the back side (inside), and a low stress on the tip 13a of the welded portion on the back surface as shown in FIG. For this reason, it becomes difficult to generate a crack from the inner surface side where the stress is low.

  Further, since the end of the flange portion 10a of the boom center boss 10 and the plate thickness of the plate material 9 are the same, it is possible to obtain a weld bead (welded portion) 14 having a smooth surface on the front side if carefully welded. It is possible to prevent a large stress from being generated on the surface of the weld. Further, since the welded portion 14 is located away from the stepped portion 15 and the plate thickness of the stepped portion 15 is smaller than the plate thickness of the collar tip portion, the stepped portion 15 has the highest stress concentration. For this reason, since the deformation of the stepped portion 15 becomes large, the stress of the welded portion 14 is relieved, and the occurrence of cracks in the welded portion 14 can be suppressed.

Although the stress of the step portion 15 of the boss 10 is increased, it is not affected by the welded portion because it is located away from the welded portion 14. For this reason, at the stage of a single part before welding the boom center boss 10, the stepped portion 15 is formed smoothly by machining or a grinder, so that stress can be applied without machining or grinder processing after welding. Since the concentration can be relaxed, the occurrence of cracks in the step portion 15 can also be prevented.
Therefore, according to the present embodiment, it is possible to prevent the occurrence of cracks on the back side (inner side) and front side (outer side) of the joint portion between the boss portion 10 and the plate member 9 and improve the strength of the joint portion.

FIG. 9 shows an example in which the above-described embodiment is applied to a boom foot boss of a hydraulic excavator, and is a cross-sectional view of the vicinity of the boom foot boss as seen from the front-rear direction.
The left and right boom foot bosses (boss portions) 17 formed with the flange portions 17 a are connected by a pipe 12, and the flange portions 17 a of the left and right boom foot bosses 17 are joined to the plate material 9 constituting the boom 3 by welding. ing. The thickness t of the plate material 9 and the thickness of the collar of the boom foot boss 17 are made substantially the same so that the acting load is transmitted smoothly at this joint.

  The boom foot boss 17 and the plate material 9 are welded with a backing material 11 for preventing blow-by on the back surface. The backing material 11 is stuck to the back surface without peeling off because the weld metal melts. For this reason, an unwelded portion 13 similar to that shown in FIG. 6 is formed between the boom foot boss 17 and the backing material 11 and between the plate material 9 and the backing material 11.

A stepped portion 15 is formed so that the flange portion 17a of the boom foot boss 17 is concave on the front side and convex on the back side.
A pin (not shown) is inserted into the hole portion of the boom foot boss 17 and is coupled to a bracket (not shown) provided on the swing frame of the upper swing body so that the boom 3 (see FIG. 1). Is attached to the upper swing body 2 so as to be freely raised and lowered. The force from the upper swing body 2 is transmitted to the boom foot boss 17 via the pin, and is transmitted from the boom foot boss 17 to the plate member 9 constituting the boom 3.

When a force is transmitted from the boom foot boss 17 to the plate member 9, a bending moment is generated due to the stepped portion 15, and when a tensile load that affects fatigue strength is applied, the stepped portion is similar to the example shown in FIG. 8. The vicinity of the portion 15 (including the welded portion) is deformed so as to bend toward the front side (outside).
Therefore, the step portion 15 has a high stress on the front side, a low stress on the back side (inside), and a low stress on the tip 13a of the welded portion on the back surface as shown in FIG. For this reason, it becomes difficult to generate a crack from the inner surface side where the stress is low.

  Further, since the tip end of the flange portion 17a of the boom foot boss 17 and the plate thickness t of the plate material 9 are made the same, it is possible to obtain a weld bead 14 having a smooth front surface, and a large stress is also applied to the surface of the welded portion. It can be prevented from occurring. Further, since the welded portion is located away from the stepped portion 15 and the plate thickness of the stepped portion 15 is smaller than the plate thickness of the collar tip portion, the stepped portion 15 has the highest stress concentration. Thus, since the deformation of the stepped portion 15 is increased, it is possible to reduce the stress in the welded portion and suppress the occurrence of a crack in the welded portion.

Although the stress of the stepped portion 15 is increased, the stepped portion 15 is not affected by the welded portion because it is located away from the welded portion 14. For this reason, stress concentration can be alleviated by forming the stepped portion smoothly at the stage of the single part before welding the boom foot boss 17, so that the occurrence of cracks in the stepped portion 15 can also be prevented.
Therefore, also in this example, the occurrence of cracks can be prevented on the back side and the front side at the joint portion between the boom foot boss and the plate material, and the strength of the joint portion can be improved.

  As described above, according to the present embodiment, the stress on the front side is high, the stress on the back side (inside) is low, and the stress on the front end of the welded portion on the back side is low. For this reason, generation | occurrence | production of the crack from a junction part inner surface side (back side) can be prevented. Moreover, according to the present Example, generation | occurrence | production of the crack from a junction part inner surface side can be prevented, without enlarging the board thickness of a board | plate material.

In the above-described embodiments, examples in which the present invention is applied to the boom center boss and the boom foot boss have been described. However, the present invention is not limited to these portions, and the boss portion at the tip of the boom or the boss portion at the tip of the arm is used. Can be applied similarly.
In this embodiment, the case where the present invention is applied to a hydraulic excavator, which is a typical work machine, has been described. However, the present invention can also be applied to various other work machines such as a crane having a structure in which a boom is attached with a pin. It is.

DESCRIPTION OF SYMBOLS 1 ... Lower traveling body 2 ... Upper turning body 3 ... Boom 4 ... Arm 5 ... Bucket 6 ... Boom cylinder 7 ... Arm cylinder 8 ... Bucket cylinder 9 ... Plate material 10 ... Boom center boss (boss part) (10a ... Boom center boss Brim)
11 ... backing material 12 ... pipe 13 ... non-welding part (13a ... non-welding part tip)
14 ... weld (weld bead) (14a ... weld bead toe)
15 ... Step part (15a ... Front side recess, 15b ... Front side step inflection start part, 15c ... Back side step inflection start part)
17 ... Boom foot boss (boss part) (17a ... Boom foot boss collar part)
20 ... Working device.

Claims (5)

In the boss structure of a working machine provided with a working device in which a boss portion is joined to the plate material by a welded portion, the plate material is configured to have a rectangular cross section
The boss part is welded to the plate member via a collar part,
A step portion is formed on the collar portion so that the front side is concave and the back side is convex, and the weld portion is provided at a position farther to the plate material side than the step portion, and on the back side of the weld portion. Is provided with a backing material for preventing the weld metal from being burned out, and an unwelded portion is formed between each of the boss portion and the backing material, and between the plate material and the backing material. The boss structure of the working machine is a feature.   2. The boss structure of the work machine according to claim 1, wherein when the plate thickness of the plate material is t, the welded portion of the welded portion is located at a position 1 t to 2 t away from the plate material side end on the back side of the stepped portion. A boss structure for a working machine, wherein the welded portion is provided so that a tip is located.   The boss structure for a work machine according to claim 1 or 2, wherein the plate thickness of the flange portion to be welded is substantially the same as the plate thickness of the plate material to be joined, and the plate thickness of the stepped portion is the weld. The boss structure of the working machine, characterized in that it is smaller than the plate thickness at the part.   The boss structure for a work machine according to any one of claims 1 to 3, wherein a back side step inflection start portion is formed closer to the welded portion than a front side step inflection start portion of the step portion. The boss structure of a work machine characterized by   The work machine boss structure according to any one of claims 1 to 4, wherein the work piece is welded to the plate member in a state in which a stress relaxation process is performed in which a step portion of the boss portion is formed smoothly in advance. Machine boss structure.

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